Every year most of the 150 million tons of plastics manufactured around the world end up in oceans, landfills and elsewhere. In the United States, less than 9% of plastics are recycled and in Europe, it rises to about 30%.
Megan Robertson, associate professor of chemical and biomolecular engineering, is coauthor of an article in the latest issue of Science, reporting that research is improving society's ability to recycle plastic waste. Credit: University of Houston
That is a $176 billion problem, the potential energy savings researchers say could be attained from recycling all global plastic solid waste. However, new approaches can increase the quantity of plastic waste that can be effectively recycled, researchers from IBM and the
University of Houston report in a perspective published in Science this week.
That means creating new plastics that are more easily recycled, together with finding ways to more effectively recycle current plastics. These approaches can vary from methods to recycle various types of plastics together in one waste stream, preventing an expensive and time-consuming sorting procedure, as well as methods to separate plastics in a more energy-efficient manner.
“Recent research points the way toward chemical recycling methods with lower energy requirements, compatibilization of mixed plastic wastes to avoid the need for sorting, and expanding recycling technologies to traditionally nonrecyclable polymers,” wrote the article authors, Megan L. Robertson, associate professor of chemical and biomolecular engineering at UH, and Jeannette M. Garcia, a polymer chemist at the IBM Almaden Research Center.
A key priority is to improve methods in order to recycle existing plastic materials.
New materials enter the market slowly, and thus the biggest impact is in developing more efficient methods to recycle the plastics that are produced in large quantities today. One the other hand, research advances can pave the way for more easily recyclable materials for the future.
Megan L. Robertson, Associate Professor, Chemical and Biomolecular Engineering, University of Houston
One example is the type of polymers called thermosets, which cannot be melted down for repurposing, avoiding their recycling with conventional methods.
Robertson’s lab creates biorenewable components for thermosets, substituting hydrocarbon-based polymers with those produced from vegetable oils or other plant-based materials. That could result in new end-of-life options such as chemical or composting recycling for these materials, a huge leap forward.
The perspective is part of a series published in Science to examine problems related to the environmental effect of polymers, including their source (biosources vs. petroleum), advances in recycling and biodegradable polymers.
Garcia and Robertson noted three key problems:
Plastics should be sorted for recycling, which includes effort and expense. Plastics, or polymers, are made up of three large molecules, so most do not mix when heated, like the interaction between water and oil. Research is aimed at finding substances that can facilitate the mixing of different types of plastics, called compatibilizers, allowing them to be recycled together. Identifying a compatibilizer that works for all types of polymers would be perfect, but Robertson stated that the current technology needs a customized approach for each plastic mixture.
Chemical recycling involves employing a catalyst to separate plastics in order to make lower-molecular-weight products, a procedure the researcher says has been hampered by high energy costs. Work to create more efficient catalysts is in progress.
Most plastics currently recycled are made up of polyethylene, the most highly generated plastic, and polyethylene terephthalate (PET), which is the component employed in most water bottles. Expanding recycling technologies to other plastics beyond polyethylene and PET is a continuing area of research. Developing methods for recycling polymers that cannot be processed through melting at high temperatures, such as elastomers (rubber materials) and thermosets, are even more challenging.
With any possible solution, the researchers say it is vital that the performance of a material is not impacted to make it easier to recycle. Subjecting plastics to various uses and recycling cycles without affecting the performance is an open challenge for researchers.
“Enhancing plastics recycling beyond the current level has many potential societal advantages, such as reducing greenhouse gas emissions, avoiding waste buildup in the environment, decreasing the dependence on finite petroleum resources for its production, and recovering the economic value of plastic solid waste,” the researchers wrote.
That has started, they say, pointing to start-up companies that have expanded chemical recycling methods for polystyrene waste or created sorting processes in order to separate materials into pure feedstocks.
That and other research, they wrote,
“raise hope that before long, recycling rates for plastics will be much higher than today.”